1. Field of the Invention
The invention relates to a steering apparatus that includes a key ring that forms a lock mechanism that restricts the rotation of a steering shaft.
2. Description of the Related Art
A lock mechanism (steering lock mechanism) is usually provided in a steering apparatus for a vehicle, as a theft-prevention measure. The lock mechanism restricts the rotation of a steering shaft, when a power source, for example, an engine is at a standstill because a switch, for example, an ignition key, an ignition knob or a push button, is off.
In this type of lock mechanism, generally, when a lock bar is inserted into a key ring that is press-fitted onto the outer periphery of a steering shaft to which a steering torque is transmitted, the rotation of the key ring is prohibited. Because the rotation of the key ring is prohibited, the lock mechanism restricts the rotation of the steering shaft using a friction force at a press-fit portion. If a steering torque that exceeds the friction force is input in the steering shaft, the steering shaft slides with respect to the key ring. The lock mechanism allows the steering shaft to rotate at a sliding torque that corresponds to the friction force and that is generated when the steering shaft slides with respect to the key ring. Therefore, it is possible to prevent damage to the lock mechanism.
In many cases, hollow shafts are used as steering shafts for reduction in weight. However, the rigidity of a hollow shaft is low. Therefore, the hollow shaft may be slightly deformed when a key ring is press-fitted onto the hollow shaft. Accordingly, if the hollow shaft on which the key ring is press-fitted is used as a steering shaft, there is a possibility that the sliding torque is not stable.
Japanese Patent Application Publication No. 2006-335165 (JP-A-2006-335165) describes an art in which a quenching process is performed on a portion of a hollow steering shaft, on which the key ring is press-fitted (and a press-fit portion of the key ring). According to this related art, the rigidity of the portion of the hollow shaft, on which the key ring is press-fitted, is increased.